1. Field of the Invention
The present invention relates to an electronic key device configured to perform predetermined control such as unlocking of doors of a vehicle by performing mutual communication between a vehicle-mounted device and a portable device.
2. Description of the Related Art
In a radio device described in Japanese Unexamined Patent Application Publication No. 2007-132139, portable means receives radio waves transmitted from a plurality of antennas provided in different positions of a vehicle, and a main control unit calculates a relative position of the portable means with respect to the vehicle based on electric field intensity measured by the portable means, and performs control such that doors of the vehicle are locked or unlocked based on the calculated relative position.
In a control system described in Japanese Unexamined Patent Application Publication No. 2012-17558, a RSSI check command is transmitted from a LF transmission unit provided at doors or a trunk of a vehicle, a RSSI value of the received RSSI check command is detected by a key, and the detected RSSI value is returned to the vehicle. In the vehicle, when the received RSSI value is equal to or greater than a predetermined threshold, the door or the trunk becomes unlocked.
However, in the radio device described in Japanese Unexamined Patent Application Publication No. 2007-132139 or the control system described in Japanese Unexamined Patent Application Publication No. 2012-17558, even when a user who does not try to enter the vehicle passes within an approach unlock area of a predetermined distance from the vehicle, there is a problem in that the doors or the trunk become unlocked.